Secondary Menu

Arduino Servo Motors

About: Inventor, Author, Head of Innovation, Entrepreneur, Forbes 30 Under 30, 10 Outstanding Young Persons of the World
More About cornelam »

Servo motors are great devices that can turn to a specified position.

Usually, they have a servo arm that can turn 180 degrees. Using the Arduino, we can tell a servo to go to a specified position and it will go there. As simple as that!

Servo motors were first used in the Remote Control (RC) world, usually to control the steering of RC cars or the flaps on a RC plane. With time, they found their uses in robotics, automation, and of course, the Arduino world.

Here we will see how to connect a servo motor and then how to turn it to different positions.

The first motor I ever connected to an Arduino, seven years ago, was a Servo motor. Nostalgic moment over, back to work!

We will need the following things:

An Arduino board connected to a computer via USB

A servo motor

Jumper wires

There are few big names in the servo motor world. Hitec and Futaba are the leading RC servo manufacturers. Good places to buy them are Servocity, Sparkfun, and Hobbyking.

This instructable and many more can be found in my Arduino Development Cookbook available here. :D

Step 1: How to Connect Them

A servo motor has everything built in: a motor, a feedback circuit, and most important, a motor driver. It just needs one power line, one ground, and one control pin.

Following are the steps to connect a servo motor to the Arduino:

The servo motor has a female connector with three pins. The darkest or even black one is usually the ground. Connect this to the Arduino GND.

Connect the power cable that in all standards should be red to 5V on the Arduino.

Connect the remaining line on the servo connector to a digital pin on the Arduino.

Check the image for a view of the servo connected to the Arduino.

Step 2: Code

The following code will turn a servo motor to 0 degrees, wait 1 second, then turn it to 90, wait one more second, turn it to 180, and then go back.

Attachments

Step 3: How It Works

Servos are clever devices. Using just one input pin, they receive the position from the Arduino and they go there. Internally, they have a motor driver and a feedback circuit that makes sure that the servo arm reaches the desired position. But what kind of signal do they receive on the input pin?

It is a square wave similar to PWM. Each cycle in the signal lasts for 20 milliseconds and for most of the time, the value is LOW. At the beginning of each cycle, the signal is HIGH for a time between 1 and 2 milliseconds. At 1 millisecond it represents 0 degrees and at 2 milliseconds it represents 180 degrees. In between, it represents the value from 0–180. This is a very good and reliable method. The graphic makes it a little easier to understand.

Remember that using the Servo library automatically disables PWM functionality on PWM pins 9 and 10 on the Arduino UNO and similar boards.

Code breakdown

The code simply declares the servo object and then initializes the servo by using the servo.attach() function. We shouldn't forget to include the servo library. In the loop(), we set the servo to 0 degrees, wait, then set it to 90, and later to 180 degrees.

Step 4: More Things About Servos

Controlling servos is easy, and here are a few more tricks we can use:

Controlling the exact pulse time

Arduino has a built-in function servo.write(degrees) that simplifies the control of servos. However, not all servos respect the same timings for all positions. Usually, 1 millisecond means 0 degrees, 1.5 milliseconds mean 90 degrees, and, of course, 2 milliseconds mean 180 degrees. Some servos have smaller or larger ranges.

For better control, we can use the servo.writeMicroseconds(us) function, which takes the exact number of microseconds as a parameter. Remember, 1 millisecond equals 1,000 microseconds.

More servos

In order to use more than one servo, we need to declare multiple servo objects, attach different pins to each one, and address each servo individually. First, we need to declare the servo objects—as many as we need:

// Create servo objects
Servo Servo1, Servo2, Servo3;

Then we need to attach each object to one servo motor. Remember, every servo motor uses an individual pin:

Connection-wise, the grounds from the servos go to GND on the Arduino, the servo power to 5V or VIN (depending on the power input), and in the end, each signal line has to be connected to a different digital pin. Contrary to popular belief, servos don't need to be controlled by PWM pins—any digital pin will work.

Continuous rotation servos

There is a special breed of servos labelled as continuous rotation servos. While a normal servo goes to a specific position depending on the input signal, a continuous rotation servo either rotates clockwise or counter-clockwise at a speed proportional to the signal. For example, the Servo1.write(0) function will make the servomotor spin counter-clockwise at full speed. The Servo1.write(90) function will stop the motor and Servo1.write(180) will turn the motor clockwise at full speed.

There are multiple uses for such servos; however, they are really slow. If you are building a microwave and need a motor to turn the food, this is your choice. But be careful, microwaves are dangerous!

Step 5: Check Out More

More topics regarding motors such as brushless, transistor drivers ormotor speed control can be found in my Arduino Development Cookbook available here. :D

Remix Contest

Weaving Challenge

Epilog X Contest

24 Discussions

for the same above code,my servo is rotating from 0 to 180 but it's not rotating back to 0, tries going beyond 180 making humming sound and keeps on doing that for ever.however if i try changing the code like starting from 180 to 0,still it rotates from 180 to 0 and doesn't come back from 0 to 180.so, can anyone help me out to solve this problem..!! ??

In his library he writes a degree to the servo and it moves there. Set up a loop that increases the degree by say... 1 every time it loops and put a delay in the loop. When you get to the position you want get out of the loop. That will get you to move in degrees per second (you can also use the millis instruction so you can do other things and not actually stop the microcontroller. The millis instruction is more complex but basically you are taking a free running clock time with millis and comparing it to the last time you got the millis instruction. This allows the controller to continue executing main and does not just stop and sit on a delay not operating the rest of the code... are you confused yet?)

One note, the on-board regulator is only good for up to 3 large servos, before you are drawing too much, that the Arduino mpu itself, begins to brown-out/reset. Then, you'll want to supply the servos externally, say with a 7805 regulator, which can still be fed from the main supply (parallel to the voltage going to the barrel socket. Highly advise against drawing through the VIn pin on the arduino, as this is still a thin trace that could burn/break)

One odd thing, despite the in-IDE example saying you can only assign 8 servo devices, ALL digital pins, 0 through 13, can be used (without serial I/O), but kinda pushing the limits.

https://www.arduino.cc/en/Main/ArduinoBoardMega The mega only has 15 PWM pins. You would probably need multiple boards with one master and two slaves communicating. As for power All you do is get a 5v power supply. Connect the ground of the power supply to the board and servos (everything must have a common ground to communicate unless you use opticouplers/relays) and use the power of the supply to the servos (it can power the arduino board too). Make sure to wire them directly to the supply. you dont want to pull all of the current through the small trace on the arduino board. Also if your arduino starts having issues when trying to run multiple servos you MAY need filtering caps to keep the noise out of the microcontroller.

Also, atleast with steppers it is difficult to control each stepper at the same time. These things work by turning a pin on and off repeatedly. If you have 48 servos that you run one after another it would not be too difficult with one board. Running multiple to different positions at the same time will be a complicated task that will take quite a bit of coding from scratch.

hello sir.I have a digital servo.my question is how to stop a digital servo completely but i want to hold the position.i have searched on arduino forum but all the topics talk about continuous rotation servos.please if you know help me sir with an example code.